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MG MGB Technical - Bad Voltage Regulator?

My 1972B seemed to be overcharging, battery lost water and it tested 14.2V @ idle, 17-18V @ 2000 rpm. So I ordered and replaced the voltage regulator with a new Lucas 2 wire unit. Now, there is absolutely no charging going on, the battery reads 12V while running. I checked out my voltmeter on another car, and it is working fine. Could I have gotten a bad voltage regulator, or is something else going on here?

This is the voltage regulator inside the alternator we are talking about?

If so sounds like you either got the wrong part, fitted it incorrectly, or it is indeed faulty.

As I recall you (maybe someone else) posted this before and I wrote about some era's of alternator having a sense wire for the voltage regulator that ran back to the solenoid. If that is faulty you could well get incorretc output from the alternator. Did you check that wire?

Also the voltage regulator is only one part of the alternator electronics, it could well be that some other part is faulty, and an exchange unit would have been a better bet.
Paul Hunt

Problem solved, I decided to replace the 37 year old alternator with one of the new Lucas units made in Turkey. Good voltage at idle, and it only increases to about 14v @ 2000 rpm. I imagine with the 45 amps (vs. 36 amp unit it replaced) I will have stronger lighting at night, the lights used to dim when I was at idle. Will try when the weather warms up around here.

All original style Lucas units seem to drop the voltage at idle, even off load, but they should still be above 12.8v even with lights and things on, rising as the revs are raised, maximum current is quoted at 6000rpm. It's one of the reasons people like to fit modern 80amp or whatever alts, as they don't drop the voltage so much at idle.
Paul Hunt

This thread was discussed between 10/04/2009 and 13/04/2009

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